The present invention relates to a cathode ray tube (CRT) display and, more particularly, to a CRT display having cathode current stabilzing means for stabilizing the cathode current.
As is well known, in a CRT display, generally, a video signal voltage is applied to a cathode electrode, and the magnitude of the cathode current is controlled synchronously with the horizontal and vertical deflection scans, thereby forming an image on the screen (fluorescent surface) of the CRT.
Converting characteristics from an input voltage of an electron gun of the CRT into an output cathode current are determined by the distance between electrodes. The converting characteristics consequently change due to a fluctuation in temperature of the electrode portion or the like, so that the fidelity of the gradations of a reproduced image deteriorates.
To prevent such deterioration, hitherto, there has been used a technique in which a black signal for detection and a white signal for detection are inserted for a vertical blanking period of a video signal, a cathode current corresponding to each of those signals is detected, and control is performed so that each cathode current always coincides with a predetermined value. The above technique is called automatic black balance and automatic white balance. Both balances are integratedly called a cathode current stabilizing system.
Reference may further be made to JP-B-55-38870 which discloses a technique to automatically correct deterioration of the black balance due to an aging effect or the like which is particularly conspicuous at portions near the black level of the signal.